Process for producing globular propellent powder grains



2,740,704 Patented Apr. 3, 1956 Crave oeur, Mo, assignors to @llnMathieson (Ihemical Corporation, a corporation of Virginia No Drawing.Application March 9, 1950, Serial No. 143,742

2 Claims. (Cl. 52-20) This invention relates generally to themanufacture of propellent powder, and particularly to the manufacture ofspherical and near spherical grains of smokeless powder.

In United States Patent No. 2,027,114, granted January 7, 1936, there isdisclosed a process of manufacturing smokeless powder wherein dropletsof lacquer, composed of smokeless powder base and solvent, aresolidified while suspended in a non-solvent medium. Such a process ofmanufacturing propellent powder has come to be known among those skilledin the art as the globular powder process. The technique of controllingthe globular powder process so as to produce grains having variousphysical and chemical properties is further disclosed in United StatesPatents Nos. 2,160,626, granted May 30, 1939, 2,213,255, grantedSeptember 3, 1940, and 2,375,175, granted May 1, 1945. These patentsdisclose variations in the basic technique of manufacturing globularpowder whereby to control the character, uniformity, and ballisticproperties of the powder produced. While the globular powder process hasproven eminently satisfactory for the production of powder grainssuitable for use in smal arms ammunition, i. e., where the diameter ofthe individual balls of powder does not exceed about ten to twenty-fivethousandths of an inch, it has not heretofore been possible to produceglobular powder grains of larger diameter, i. e., greater than abouttwentyfive thousandths of an inch, on a mass scale.

While it has heretofore been known, as pointed out in some of thepatents above-mentioned, that control of the violence of agitation hasits efiect upon the granulation of the productthe more violent theagitation the smaller the grains and vice versait has not heretoforebeen possible to produce batches wherein more than a small percentage ofthe grains were of large diameter and well rounded. Efforts to producelarge diameter grains by reducing the speed of agitation of the usualglobular powder equipment have resulted in batches of grains,practically none of which were sufliciently spherical to meet thecriteria set for globular powder.

The object of the present invention, generally stated, is to provide aprocess of producing globular powder grains of large diameter andwherein the yield of each batch is predominantly of large diameter.

A further obiect of the invention is to provide a process ofmanufacturing globular powder wherein the granulation may controlledwith greater uniformity than heretofore.

Qther objects will become apparent to those skilled in the art when thefollowing description is read:

The invention contemplates the production of globular powder grains, byprcsizing (as to volume) bodies of powder ease lacquer, then suspendingthe bodies in a non-solvent medium until they become rounded; and then,while in their rounded condition, hardening them. The presized bodiesare composed essentially of a solution of the powder base in a solventwhich is substantia iy immiscible with the non-solvent medium, saidsolution being of a consistency such that the bodies are selfsustainingand self-coherent under the forces to which they are subjected while insuspension.

The presizing of the bodies to the volume which will yield spheres ornear-spheres of the desired size, when hardened, may be accomplished inany of a variety of ways.

Bodies of sufficiently uniform volume may be produced in the apparatusemployed for the manufacture of ordinary globular powder by agitating acurd of the high viscosity lacquer in a non-solvent medium andcontrolling the violence of the agitation to regulate the size of thebodies into which the curd is disintegrated, it being understood thatthe more violent the agitation, other variables being constant, thegreater the degree of disintegration. Presizing the bodies in thismanner to produce a high yield of large diameter grains requires thatthe viscosity of the lacquer be so high that the grains of 0.025 inchdiameter or greater do not properly shape without further treatment toreduce their viscosity.

While the presized bodies are suspended in the nonsolvent medium, it isimportant that the forces of agitation be only suilicient to maintainthe suspension, and

not of such violence as to subdivide the suspended bodies.

Some subdivision and some coalescence of initially separate bodies isalmost inevitable, but such are minimized by the precautions followed inthe manufacture of globular powder generally, including in particularthe addition of a protective colloid to the suspension.

Since the presized bodies of size such as to yield grains of 0.025 inchdiameter or greater, when first suspended, are of consistency such thatthey do not readily yield under the interfacial tension exerted in thesuspending medium, to approach the spherical shape, their viscosity isreduced, as by the introduction of some additional solvent into thesuspending medium; said solvent, being not mutually soluble with themedium, is absorbed by the suspended bodies and softens them.Alternatively, the presized suspended bodies may be further softened byheating under pressure sufiicient to inhibit vaporization of thesolvent.

After the softening treatment, the bodies begin to yield to the forcesof interfacial tension in the medium, and ultimately assume thespherical shape. Thereupon the solvent is removed from the bodies, whilemoderate agitation continues.

As an illustrative example of the process, a body of lacquer composed of3.8 parts of ethyl acetate to each part of nitrocellulose, with theusual stabilizers, was disintegrated at a temperature of 68 C. in awater bath containing the solutes and colloids commonly used in themanufacture of globular powder. The disintegration was accomplished bymoderate agitation (viz. at 32.5 R. P. M. with the device usuallyoperated at 40 R. P. M. for the production of ordinary globular powder).The suspended bodies would not round by any of the usual techniques.

While the presized but misshapen lacquer bodies were in suspension,ethyl acetate was added to the water bath in the amount of 10% of theweight of the nitrocellulose. The additional ethyl acetate wasintroduced into the water bath as an emulsion, consisting of 40 partsethyl acetate, 120 parts water, and 2 parts protective colloid. Theagitation was reduced to 28.75 R. P. M. and continued for one andone-half hours, when the bodies were adequately rounded.

The resultant grains were nearly perfect spheres, with 58 per cent ofthe yield having a diameter greater than 0.0276 inch. Slower agitationspeeds at the time of presizing result in an increase of the grain size,for example, whereas the product just mentioned was presized at 32.5

0 R. P. M., when the presizing is at 30 R. P. M., 79 per cent of theyield has a diameter greater than 0.0276.

Instead of introducing the additional solvent in the formof an emulsion,asin'the last example, it can be added inundilutedform gradually to thewater bath,-

provided it is finely dispersed-in the water bath.

From the foregoing descriptiom those skilled in the art sliould'understand that the invention accomplishes itsway oflimitation, I It isrecognized that those skilled in the=art will make appropriateadjustment of the'several variabl'esi'n the process in-order to-adaptitto the peculiarities of any given operation, and consequently it isto-bei distinctly understood that the invention is not limited to= theexamples given, save as indicated in the appended claims.

Havingthusdescribed the invention, what is claimed and desired to besecured by Letters Patent is:

1. In" the manufacture of globular grains of propellent powder, theprocess of making grains having a diameter of. atuleast 0.025v inch,comprising, presizing bodies. of

propellent powder base lacquer and suspending the prev sized bodies in anon-solvent medium, then thereafter,

while the presized bodies remain so suspended, reducing the viscosity ofthe lacquer in thepresized bodies, maintaining such reduced viscosityuntil the bodies approach spherical shape, and then, hardening theshaped bodies, all while suspension is maintained.

2. The process of claim 1 wherein the presizing is accomplished byagitation of a curd of lacquer within the non-solvent medium.

References- -Cited in the file of this patent UNITED STATES PATENTS2,027,114 Olsen et a1. Jan. 7, 1936 2,160,626 Schaefer May 30, 1939.2,206,916 Olsen et al, July 9, 1940 2,213,255 Olsen et al. Sept. 3, 19402,230,848 Regestein Feb. 4, 1941 7 2,299,929 Ray-nolds, Jr. Oct. 27,1942 2,375,175 Silk Mayv 1, 1945

1. IN THE MANUFACTURE OF GLOBULAR GRAIS OF PROPELLENT POWDER, THEPROCESS OF MAKING GRAINS HAVING A DIAMETER OF AT LEAST 0.025 INCH,COMPRISING, PRESIZING BODIES OF PROPELLENT POWDER BASE LACQUER ANDSUSPENDING THE PRESIZE BODIES IN A NON-SOLVENT MEDIUM, THEN THEREAFTER,WHILE THE PRESIZED BODIES REMAIN SO SUSPENDED, REDUCING THE VISCOSITY OFTHE LACQUER IN THE PRESIZED BODIES, MAINTAINING SUCH REDUCED VISCOSITYUNTIL THE BODIES APPROACH SPHERICAL SHAPE, AND THEN HARDENING THE SHAPEDBODIES, ALL WHILE SUSPENSION IS MAINTAINED.